This invention concerns improvements in and relating to monitoring, particularly the monitoring of radiation dose and dose rate.
Three principle ways of expressing radiometric measurements exist, namely activity, count and dose.
In general terms activity is a measure of the amount of radioactive material present within an environment. Activity is measured in Becquerels (Bq) where 1 Bq is 1 nuclear disintegration per second.
Counts relate to the counting rate of a radiation detector, such as a scintillator, in a gamma flux. The count rate equates to the number of gamma photons depositing some energy in the detector in each second. By recording such information over a period of time a recorded spectrum relating to the given energy range is obtained.
Dose relates to the interaction of gamma rays with living tissue. Dose is a measurement of the energy deposited in the tissue by gamma ray flux and is measured in Sieverts (Sv) where 1 Sv is 1 Joule per kilo. Dose relates to a specific spatial point and is derived from all gamma rays arriving at that point. Dose rate is proportional to the number and energy of the gamma photons arriving at a point in a second. Dose and dose rate measurements are of fundamental importance in the nuclear industry and in other radiological environments as they are the basis of most health and safety legislation relating to working environments and exposure.
Instruments exist which allow the determination of dose at a point in space. However, each such system relies on a detector for gamma flux being presented to the particular point for which the dose or dose rate determination is required. Thus in determining the dose or dose rate variation for a substantial volume a very large number of measurements are required. Unfortunately, the dose at any one particular point is unrelated to the dose at other points within an